Defender (13)
'defender' is the definition.
(I know that defender can be written as guardian)
This is the entire clue.
(Other definitions for guardian that I've seen before include "Protector or watchful angel" , "Protector, keeper" , "Champion - paper" , "Platonic leader" , "Type of angel" .)
(Other definitions for guardian angel that I've seen before include "spirit of helpfulness" , "Benevolent spirit" , "Person concerned with the welfare of another" , "Person keeping an eye on one's safety (including a newspaper)" , "Friendly spirit" .)